Actor James Gandolfini’s death at age 51 from an apparent cardiac arrest while in Rome shocked fans and friends alike. But sudden cardiac arrest, a misunderstood term, is all too common, cardiologists say.

The "Sopranos" actor was taken from his hotel in Rome to Umberto I hospital, where 40 minutes of doctors’ efforts to revive him -- including massaging his heart -- were unsuccessful, emergency room chief Dr. Claudio Modini told Reuters.

"Here’s a guy that died at a very young age," said Dr. Robert Kloner, director of cardiac research at Good Samaritan Hospital in Los Angeles. "It’s very sobering."

There are several risk factors for cardiac arrest, including gender (men are somewhat more at risk), obesity, smoking, high blood pressure and a history of coronary artery disease.

While cardiac arrest is frequently confused with the term "heart attack," the two terms are not interchangeable, Kloner pointed out. According to the American Heart Assn., a heart attack is caused by blocked blood flow to the heart, typically by the buildup of plaque on artery walls; but in sudden cardiac arrest, the heart suddenly and unexpectedly stops beating.

“Most people who have [sudden cardiac arrest] die from it — often within minutes,” according to the National Heart, Lung and Blood Institute. Cardiac arrest can be caused by a number of different heart issues, including certain types of arrythmia -- a misstep in the heart cells’ beating rhythm -- or by a heart attack, known formally as a myocardial infarction.

A heart attack, on the other hand, can show symptoms days or even weeks in advance, according to the Mayo Clinic. Symptoms include nausea, shortness of breath and crushing chest pain.

While cardiac arrest and heart attacks are two separate phenomena, a heart attack can play a role in sudden cardiac arrest, Kloner explained.

"Some cases of sudden cardiac death occur in the setting of a heart attack, in which the coronary artery is [blocked], the heart muscle doesn’t get enough oxygen, the heart muscle cells become electrically unstable and an arrythmia occurs,” Kloner said.

More complete answers into what led to Gandolfini's death will have to wait until the autopsy, which is scheduled for Friday, Modini said.